GPS alignment data during IRU/IRS alignment—why used?

GPS alignment data during IRU/IRS alignment—why used?

• A. To calibrate the air data computer.
• B. To configure the weather radar.
• C. To establish accurate attitude and heading references.
• D. To determine cabin pressure altitude.

Answer: (C)

The idea being tested is how GPS data is used to bootstrap the inertial sensors to give a trustworthy attitude and heading reference. The inertial reference unit measures rotation and acceleration, but without a known initial orientation its outputs drift over time. By bringing in GPS information—position, velocity, and the direction of travel—the system can determine the aircraft’s true track relative to the Earth and align the body axes to the Earth axes more accurately. This external reference lets the IRS solve for any misalignment between the aircraft frame and the Earth frame, establishing the initial roll, pitch, and especially heading quickly and with higher accuracy. The advantage is faster, more reliable alignment that reduces drift once in flight. This approach isn’t about calibrating the air data computer, configuring weather radar, or determining cabin pressure altitude, which rely on different sensors and systems.

The idea being tested is how GPS data is used to bootstrap the inertial sensors to give a trustworthy attitude and heading reference. The inertial reference unit measures rotation and acceleration, but without a known initial orientation its outputs drift over time. By bringing in GPS information—position, velocity, and the direction of travel—the system can determine the aircraft’s true track relative to the Earth and align the body axes to the Earth axes more accurately. This external reference lets the IRS solve for any misalignment between the aircraft frame and the Earth frame, establishing the initial roll, pitch, and especially heading quickly and with higher accuracy. The advantage is faster, more reliable alignment that reduces drift once in flight.

This approach isn’t about calibrating the air data computer, configuring weather radar, or determining cabin pressure altitude, which rely on different sensors and systems.